Radio-ulnar synostosis is one of the congenital malformations of the elbow joint that can be severely disabling, especially if it is present bilaterally or there is marked hyperpronation. In the case of fixed pronation of 60 degrees or more corrective surgery is definitely indicated to reduce functional impairment. As yet, there is no standard operative procedure for restoration of useful supination/pronation function of the forearm. Derotational osteotomy at the site of synostosis seems to be the best procedure. As the postoperative aim we recommend fixed pronation at 15 degrees -35 degrees for the dominant hand and fixed supination at 15 degrees -30 degrees for the contralateral hand. Major derotational procedures should be performed in several stages to avoid neurovascular complications.